Can a preacher or teacher accomplish anything without God opening the heart?
No minister or teacher can accomplish anything unless the Lord opens the heart. In Acts 16, God opened Lydia's heart so she attended to Paul's words; Paul was the instrument, but God did the opening. The same principle applies today: believers are instruments God can use when He opens a heart to receive His Word.
The context points to Acts 16, where Lydia, a seller of purple from Thyatira who worshiped God, heard Paul and the others. Scripture says the Lord opened her heart so that she attended to the things spoken by Paul. The context then asks who opened Lydia's heart—God did—and what instrument God used to attend to her need. It applies this same pattern today: no minister or teacher can accomplish anything unless the Lord opens the heart. That is why prayer is appreciated, not only for the teacher but for everyone who passes these things on. The main thing is that believers are instruments God can use when He opens a heart so somebody can give Him the Word. The context also notes a rare discussion where some claimed to have found salvation absolutely by themselves without any outside input, but it says this is very, very seldom.